1. Field of the Invention
The present invention is concerned with a microorganism. More specifically, the present invention relates to a process for producing an L-amino acid through fermentation, and a DNA and a microorganism which are used in this process.
2. Description of Related Art
When L-lysine is produced through fermentation, strains separated from the natural field or synthetic strains thereof are used to improve the productivity. A large number of L-lysine-productive synthetic mutants are known, and many of them are aminoethylcysteine (AEC)-resistant mutants belonging to the genus Brevibacterium, Corynebacterium, Bacillus or Escherichia. Further, transformants obtained upon using recombinant DNAs are also employed (U.S. Pat. No. 4,278,765). Thus, a variety of technologies for increasing the productivity of amino acids are disclosed.
For example, with respect to the genus Escherichia, a process for producing L-lysine by enhancing a dihydrodipicolinic acid synthetase (hereinafter abbreviated at times as "DDPS") is described in Japanese Laid-Open (Kokai) No. 18,596/1981, U.S. Pat. No. 4,346,170 and Applied Microbiology and Biotechnology 15, 227 (1982).
The dihydrodipicolinic acid synthetase (DDPS) is an enzyme that catalyzes dehydro-condensation of aspartosemialdehyde and pyruvic acid to form dihydrodipicolinic acid. This release feedback inhibition with lysine is disclosed in International Laid-Open Pamphlet WO95/16042.
When L-threonine is produced through fermentation, strains separated from the natural field or synthetic mutants thereof are used as microorganisms. A large number of L-threonine-productive synthetic mutants have been known, and many of them are resistant to .alpha.-amino-.beta.-hydroxyvaleric acid, belonging to the genus Escherichia, Serratia, Brevibacterium or Corynebacterium. With respect to the genus Escherichia, a process for producing L-threonine using a strain transformed with a recombinant plasmid containing a threonine operon is described in Japanese Laid-Open (Kokai) Nos. 131,397/1980, 31,691/1984 and 15,696/1981 and Japanese Patent Announcement No. 501,682/1991.
Further, a process for producing L-threonine using E. coli containing lysC that has mutation by which to release feedback inhibition with lysine is disclosed in International Laid-Open Pamphlet WO94/11517.